The present invention relates to a centrifugal pump for feeding pulverized material from a low pressure zone into a high pressure zone. In particular, the present invention relates to a centrifugal pump for pulverized material that includes a hollow rotor with a central chamber communicating with a plurality of channels extending toward the outer rim of the rotor, each channel communicating at the outlet thereof with a nozzle.
Such centrifugal pumps are used for feeding pulverized material, such as coal particles, and granulated reactants and/or catalysts into vessels such as furnaces and reactors wherein the pressure of the gas present therin is higher than the pressure in the space from which the pulverized material is to be transferred into the vessel.
Processes wherein centrifugal pumps for pulverized material may find useful application are, for example, coal gasification, coal combustion under pressure, supercritical gas extraction, iron ore reduction with solid fuel injection, feeding of catalyst to a catalyst cracking unit, and feeding of limestone or dolomite to a sulphur removal installation under pressure.
In operation, the outlet of the centrifugal pump communicates with a space wherein a high gas pressure prevails. The pulverized material that is to be introduced into this space, is supplied to the central chamber of the hollow rotor of the pump. Under the influence of the centrifugal forces exerted by the rotating rotor on the pulverized material, the material is displaced outward at great force and enters the channels leading to the outer rim of the rotor. Such channels may be placed radially with respect to the center of the rotor and have a cross-sectional area that changes in radial direction from a rectangular shape to a circular shape. The pulverized material is ejected from each channel into the high pressure space via a nozzle that is carried by the rotor and placed coaxially to the channel with which it cooperates.
A centrifugal pump of the above-described type is known from PCT patent application No. W 80/00407 in the name of Lockheed Missiles & Space Co. Inc. (filed Apr. 10, 1980, published Nov. 13, 1980). The feed rate of the material through the nozzles of the centrifugal pump described in this publication is controllable by controlling a supply of gas under pressure to the interior of the nozzle.
The material flow through the nozzles is in the form of mass flow. In this type of flow, these are no stagnant zones, and movement of the particles at the outlet of the nozzles implies movement of all other particles present in the nozzles. The interior of each nozzle through which mass flow takes place is of frusto-conical shape, and the apex angle of the cone of which the frusto-cone forms part is relatively small. Consequently, the length of the cone is relatively large.
In view of the extremely high rotational speeds at which the rotors of centrifugal pumps for pulverized material are operated, it is desirable to decrease the overall diameter of such rotors, since such decrease in diameter will result in lower energy consumption of the electric motors that drive the pump rotors.
It has been found, however, that shortening the length of the nozzles to obtain a rotor with relatively small diameter, negatively influences the control of the flow rate of the material through the nozzles.